Ignoring engine layouts such as V6’s and V8’s which don’t lend themselves to powering your VW for size shape and weight reasons, the following possibilities are left:

In Line 4 or 5 Cylinder Engines – these are only really suited to the VW’s with larger engine bays, such as type 2’s, type 3’s (if you don’t mind losing most of your luggage space), type 25 / Vanagon’s, and Karmann Ghia’s. In type 2’s the choice is limited to water cooled tilted in line fours due to an upright four cylinder engine being too tall to fit into the engine bays designed for a horizontally opposed (flat) four cylinder. The most common in line four engines used for such conversions are the ‘80’s and ‘90’s VW models. Some of these were mounted tilted, and others which were originally mounted upright can be converted to a tilted installation by using parts from various other models with tilted engines.

Late model Type 25 / Vanagon models built in South Africa up until 2000 featured in line four and five cylinder engines, many of which were Audi based, mounted upright. They relied on this model’s long engine bay and some extra height ‘stolen’ from the luggage area behind the rear seats to get it all to fit in (just). It may be possible to copy this conversion using parts from the VW / Audi range, but little is known about exactly what parts are needed. The South African spec (genuine VW) bellhousings are still available, as is the engine support bar.

Probably the best is inline tilted four engine option is the modern VW / Seat / Skoda TDi diesels, with no air cooled options. Again, there is little information around on how to do this conversion, and relatively few have been done. With power from the latest spec engines being over 150 bhp, they certainly seem like a good engine for your VW. Installing a TDi engine is a very big job. As well as exhaust plumbing to sort out, the intercooler installation is a major job, and is likely to be compromised due to a lack of cold air to feed it. Their use will be limited to VW’s with large engine bays. The TDi engines are relatively expensive, and the finished installation is not particularly neat – it does not ‘look the part’. Also, to most people there is no choice between petrol and diesel - they either want one or the other.

Non of these in line four / five cylinder conversions really look like they ought to be in most VW’s which were originally designed for a horizontally opposed (flat) four cylinder engine. They always look like a conversion (even the ‘factory’ South African models, with their ‘raised box’ in the engine access cover to clear the cylinder head), and most VW owners prepared to convert their vehicles are looking for something neater.

Horizontally Opposed 4 or 6 Cylinder Engines – there are air and water cooled options here. Your air cooled options are limited to Porsche flat fours, or Porsche or Chevy Corvair flat sixes. The Porsche flat fours are a bolt on conversion, but are generally not considered viable as a modern tuned VW flat four will both be cheaper and produce more power.

Flat six options can be made to work in busses, Karmann Ghia’s or Type 3’s, with their large engine bays, but are not really suited to Beetles, as they require major external body mods. This is despite the widely believed story amongst the uninformed that a Porsche flat six fits straight into a Beetle! The Corvair engine is too old a design to be considered an upgrade for the VW (and spins ‘backwards’, so needs a reverse rotation cam shaft, etc), and Porsche engines are too expensive (and maybe too powerful - if there is sucha thing!) for what a lot of people want. Although those from before ’96 are all air cooled, so require no radiator, they are all dry sumped, so need a complex external oil system, requiring as much or more work to install in your VW as a radiator system. In the eyes of many people, Porsche engines remain the ultimate option, but most can not afford them though!

Water cooled horizontally opposed engine options include Alfa and Subaru flat fours. The Alfa flat fours, as with Chevy Corvairs, are too old to be considered a viable upgrade to your VW. They can be made to fit into busses, Karmann Ghia’s or Type 3’s, and can just about be made to fit into Beetles, but are very wide, so require some body mods.

This Leaves One Option – Subaru:

Subaru have been producing horizontally opposed engines for nearly 40 years. Pushrod designs were used up to 1989, but again these are considered to be too old to be viable as an upgrade for your VW, despite having a reputation for being indestructible. The new range of engines introduced in 1990 are all either single or double overhead cam designs (SOHC or DOHC). There is a huge choice of capacities and performance options, and therefore typical prices too. They are also very compact – the basic four cylinder ‘long block’ can be made to fit into just about any VW neatly, and the some of the six cylinders can be made to fit certain VW’s very neatly too.

Subaru engines are the best option all around if you are looking to update the performance and economy of your VW. Subaru are also working in conjunction with Saab on the first all alloy horizontally opposed diesel engines - can’t wait to get those into VW’s - they can’t come soon enough!